WASHINGTON, Jan 31 (Reuters) - Boeing Co was awarded a $6.56 billion U.S. defense contract for development and sustainment of an enlarged ground-based midcourse anti-ballistic missile defense system, the Pentagon said on Wednesday.

The Pentagon said the contract accelerates "delivery of a new missile field with 20 additional silos and two additional silos in a previously constructed missile field at Fort Greely, Alaska." The contract runs through December 2023.

Earlier on Wednesday, Boeing Chief Executive Dennis Muilenburg said the company had met "our commitment to the Missile Defense Agency to have 44 ground-based interceptors in place by the end of 2017." Wednesday afternoon's award was for a planned expansion of capabilities at Fort Greely.

Within the U.S. Department of Defense the Missile Defense Agency (MDA) is charged with the mission to develop, test and field a ballistic missile defense system.

MDA systems have multiple layers and ranges and use sensors in space, at sea and on land that altogether form a defense for different U.S. regions and territories. The ground-based midcourse system was designed to knock down Intercontinental Ballistic Missiles, which could be launched from North Korea or Russia. "We're honored to support the U.S. military in protecting the homeland," Boeing Defense tweeted in reaction to the award. Boeing on Wednesday forecast full-year profit well above Wall Street estimates as it looks forward to its busiest year ever for plane deliveries, sending its shares up almost 5 percent. (Reporting by Eric Beech and Mike Stone; Editing by David Alexander and Susan Thomas)